JPS60100113A - Laser beam printer - Google Patents

Abstract

PURPOSE:To prevent deteriotation of a picture quality caused by a temperature variation by detecting a focus shift, and moving a correcting convex lens in the optical axis direction in accordance with this shift quantity. CONSTITUTION:When an atmospheric temperature is varied, a refractive index of a plastic lens 2 is varied. A passing light of a cylindrical lens 8 made of glass is varied by a focal variation, and each signal detected by a four-divided photodetector 9 is compared and amplified by a differential amplifier 10. Its output is applied to a motor 13 of a moving device 3b, and a correct focal position is obtained by moving a focal position correcting convex lens 3a in accordance with its shift quantity. In case when the focal position is shifted to a distance from a photosensitive body 7 due to a temperature rise, the focal position adjusting convex lens 3a is moved in the direction of a collimator lens 2 made of plastic on the optical axis by the moving device 3b. In case when a temperature has dropped, it is moved in the direction opposite to them.

Description

Detailed Description of the Invention Field of Sedentary Work The present invention scans a light beam using a plastic lens optical system and a rotating polygon mirror to form an electrostatic latent image on a photoreceptor, and visualizes the latent image to form an image. The following is related to laser beam printers.

Conventional technology In general, compared to glass lenses, plastic lenses have the advantage of being easier to produce an aspherical surface and are cheaper to manufacture. When used in a laser beam printer, the focal position changes depending on the temperature, which causes the beam diameter on the photoreceptor surface to change, resulting in a deterioration in image quality.

The object of the present invention is to overcome the above-mentioned drawbacks and to provide a laser beam printer with good image quality and low cost.

The invention relates to a laser beam printer in which a beam from a semiconductor laser is scanned onto a photoreceptor through a rotating polygon mirror and a lens system, in which a portion of the beam scanned onto the photoreceptor is received. A focal shift detection means for detecting a focal shift, a differential amplifier for comparing and amplifying the signal of the detection means, and a lens moving device disposed at an appropriate position on the optical axis and movably attached to a lens for correcting a focal shift. and an output corresponding to the amount of defocus detected and amplified by the detection means is input to the lens moving device, so that the correcting convex lens can be moved along the optical axis direction. It becomes.

Example Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a laser beam printer of the present invention, in which the beam output from a semiconductor laser 1 is focused by a plastic collimator lens 2, and after passing through a convex lens 6a for adjusting the focusing position N, a rotating polygon @ 4 reach. The convex lens 6a for focal position adjustment is a lens moving device '3b.
There are several lines at the top, and it can be moved back and forth on the optical axis.

The beam scanned by the rotating polygon mirror 4 passes through a plastic Fθ lens 5 and then focuses on the photoreceptor B. Reference numeral 7 is a mirror for taking out a part of the scanned beam, and the beam polarized by this mirror 7 passes through a cylindrical lens 8 made of optical glass, and then is sent to the defocus detection means ff1J, which is the 4-split light receiving element 2. It is incident.

If the focal position is not shifted, the beam extracted by the mirror 7 passes through the cylindrical lens 8 and reaches the four-split light receiving element 9, where it is received in a circular shape as shown in Fig. 2(a), but if the atmospheric humidity is 2f. When the temperature changes, the refractive index of the plastic lens changes, so that the beam, which was focused on the surface of the photoreceptor 6 when the film temperature was near, shifts its focal position. Due to the shift in the focal point position due to this 1til u change, the beam passing through the optical glass cylindrical lens 8 will be incinerated in the shape of its Hji surface, so it will take 4 minutes. 1] Light receiving element 9
By detecting changes in the elliptical shape as shown in FIG. 2, it is possible to detect a shift in the focal position of the beam.

Next, the shift in the focal position is detected by applying the output from each of the four divided signals to the motor 16 of the 18-movement device tt3b using the differential amplifier 10. Convex lens 3 for correcting the fish point position depending on the amount of deviation
By shifting a, an appropriate focal position can be obtained.

For example, when the temperature rises, the focal position changes on the photoreceptor 7.
Convex lens 6 &
may be moved along the optical axis in the direction of the plastic collimator lens 2 by the moving device 6b, and if the temperature drops and the focal position shifts toward the front of the photoreceptor 7, it may be moved in the opposite direction.

FIG. 2(B) shows the light receiving state when the light is shifted to the far side, and FIG. 2(Q) shows the light receiving state when the light is shifted to the front.

FIG. 6 shows a specific example of the lens moving device 6b, and its configuration includes two guide holes 15, 15 arranged in parallel, a screw shaft 11 with a spiral groove, and a rotation of the screw shaft 11. It consists of a lens holder 12 that moves in parallel with the lens, a motor 16 that rotates the screw shaft 11, and a support 14.

As mentioned above, in this embodiment, the focal position adjustment lens is a convex lens, but this is not necessarily the case, and a concave lens or a combination thereof may also be used. You can get the same effect by placing it immediately after.

Effects of the Invention As detailed above, in the present invention, in a laser beam printer having a plastic lens system, a defocus detecting means for receiving and detecting a part of the beam scanned on a photoconductor is used. Since a lens moving device with a convex lens is provided to automatically correct the focal position deviation, it is possible to eliminate deterioration in image quality due to humidity changes and to reduce costs. You can get a laser printer.

[Brief explanation of the drawing]

] (Figure 11 is the head office) Schematic diagram showing the embodiment of Ming, Figure 2 (
a), (b), and (Q) are diagrams each showing the state of light reception of the beam to the four-split light-receiving element.
Figure 11747, with extra figures inside. 1... Semiconductor laser 2... Plastic collimator lens 6a... Convex lens for focal position adjustment 6b... Lens moving device 4... Rotating polygon mirror 5... Fθ convex lens... Photoreceptor 7... Mirror 8・・Glass cylindrical lens 9・・4-split receiving element 10・・Differential amplifier 11・・Screw shaft 12・・Lens holding stand 1・・Motor 14・・Support stand Fig. 3

Claims (1)

[Claims] In a laser beam printer in which a beam from a semiconductor laser is scanned onto a photoconductor via a rotating polygon mirror and a lens system, a defocus detecting means detects a part of the beam scanned onto the photoconductor; , comprising a differential amplifier for comparatively amplifying the signal of the detection means, and a lens moving device disposed at an appropriate position on the optical axis and movably attached to the defocus correction lens, A laser beam characterized in that an output corresponding to the amount of defocus detected and amplified by the detection means is input to the lens moving device, so that the convex correction lens can be moved along the optical axis direction. printer.